Method of making a reference voltage source with a desired temperature coefficient

ABSTRACT

A temperature stability of a high order is obtained by voltage divider trimming in a circuit in which a common current supply feeds a first branch containing one or more Zener diodes and a second branch containing a voltage divider composed of ohmic resistances, from the tap of which the output voltage is taken, by provision of a circuit configuration meeting one design criterion and trimming an output voltage divider to meet, at a single reference temperature, another design criterion and thus to set both the designed output voltage and the designed temperature coefficient, independently of the scatter of the characteristics of the diodes in the circuit.

United States Patent Conzelmann et a1. Nov. 4, 1975 METHOD OF MAKING A REFERENCE 3,582,688 6/1971 Hilbert 1. 307/235 R VOLTAGE SOURCE mm A DESIRED 3,612,984 10/1971 Davis et a1. 323/22 T TEMPERATURE COEFFICIENT 3,743,850 7/l973 Da is 323/4 X [75] Inventors: Gerhard Conzelmann, Leinfelden; OTHER PUBLICAUONS Hartmut Seiler, Reutlingen, both of Kesner, Monolithic Voltage Regulators," IEEE Spec- Germany trum, April 1970, pages 24, 2628. Chu et al., A New Dimension to Monolithic Voltage [73] Asslgnee' ggmz GmbH Stuttgart Regulators, IEEE Transactions, Vol. BTR-lS, N0. 2,

y May 1972, pg. 73. [22] Filed: Mar. 4, 1974 21 A L NO; 447,514 Primary Examiner-A. D. Pellinen 1 pp Attorney, Agent, or Firm-William R. Woodward Mar, 23, 1973 Germany 2314423 A temperature stability of a g Order is Obtained y voltage divider trimming in a circuit in which a com- [52] mon current supply feeds a first branch containing one [51] Int Cl 2 HOIL 605}: or more Zener diodes and a second branch containing [58] Fie'ld 307/235 R 318, 323/1 a voltage divider composed of ohmic resistances, from 323/4 8 22 T 22 the tap of which the output voltage is taken, by provi- 3 6 sion of a circuit configuration meeting one design criterion and trimming an output voltage divider to meet, at a single reference temperature, another design cri- [56] Referencm cued terion and thus to set both the designed output voltage UNITED STATES PATENTS and the designed temperature coefficient, indepen- 1983,863 5/ 1961 Keonjian 323/22 T dently of the scatter of the characteristics of the di- 3,282,631 11/1966 Mosinski 307/318 x Odes in the Circuit 3,497,794 2/1970 Fredrickson et all. 323/22 T 3,534,245 10/1970 Limberg 323/4 23 Cl lm 1 Drawing Flgures m U LU l l D. C. R SOURCE U k- U l l U.S. Patant Nov. 4, 1975 Sheet 1 of5 3,916,508

Z-UD I I J an. R 1 1 1 SOURCE U 1 U.S. Patent Nov. 4, 1975 Sheet 2 of 5 3,916,508

US. Patent Nov. 4, 1975 Sheet 3 of5 3,916,508

Sheet 5 of5 3,916,508

US. Patent Nov. 4, 1975 METHOD OF MAKING A REFERENCEVOLTAGE SOURCE WITH A DESIRED TEMPERATURE- COEFFICIENT The invention relates .to a method ofv making source of reference voltage having a desired high stability with respect to temperature or a desired temperature coefficient of voltage.

It is known to make a source of reference voltage with a parallel connection of two current carrying circuit branches the first of which contains a Zener diode and the second a series connection of two ohmic resistances and of two conductively poled diodes connected together in series. The reference voltage is taken from this circuit between the common connection point of the two ohmic resistances and that one of the common points of the two current branches at which the Zener diode is connected with the second conductively operated diodes. The voltage divisionratio of the two ohmic resistances is constant, so that the reference voltage source has the exact desired temperature coefficient only for a single value of Zener breakdown voltage. But since the breakdown voltage of Zener diodes is subject to an unavoidable scatter in values as the result of the operation of the processes of manufacture, the above described known circuit provides a reference voltage that has a relatively large scatter of the values of the temperature coefficients of individual units.

It is an object of the invention to provide a method of making source of reference voltage in such a manner that the temperature coefficient of the reference voltage supplied by the source takes on a predetermined value which is independent of the scatter effects caused by manufacture.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the number of Zener diodes used in cascade and the number of conductively operated diodes used in series respectively with the Zener diodes and with the voltage divider resistors is selected to fit a formula found to give superior temperature stability and then the resistances of the voltage divider are trimmed in such a manner that the temperature dependence of the reference voltage meets another criterion further described below.

The first formula, stating a condition to be met according to the invention, is in terms of k, the number of Zener diodes in cascade, which is at least I; the number l of conductive diodes in series with the Zener diodes, which may be the number m, which may be 0, of conductive diodes connected in seriesvwith the voltage divider and connected on that side of the voltage divider where the voltage drop is not included in the output voltage, and the number n of conductive diodes in series with the voltage divider and connected on the other side of the voltage divider (where the voltage drop is included in the output voltage), which number is at least 1. The formula in question is I is the voltage drop at the reference temperature To for the conductively driven diodes, in volts, A is the constant portion of the temperature coefficient of th Zener diodes in K, A is the temperature coefficiel in K of the-conductively poled diodes when conduc ing and E is the desired temperature coefficient of ti". reference voltage U likewise in "l( and A is the ten perature coefficient in "K of the diodes operated i their conducting state. Their relation with reference 1 Which the voltage divider is balanced by trimming tl". voltage divider is as follows In a further development of the invention, the voltag drop per diode U and the temperature coefficient A of the diodes operated in their conducting conditio can be chosen in such a manner that the equation fir above mentioned is satisfied, not merely approx mately, but exactly. The quotient on the right hand sic' of this equationthen becomes a whole number (ll'ltt ger). Particularly in the case of a voltage referent source made on a silicon substrate the particular nun bers represented in the formula by l, k, m and it may 1: chosen to satisfy at least approximately the relation In the method of the invention the division ratio the voltage divider at a predetermined reference ten perature To is modified progressively by trimming th resistors of the voltage divider until the reference vol age U, at this reference temperature To reaches a fixe predetermined'value given by the expression A A |n=r1' m The invention will be further described by way of e: ample with reference to the accompanying drawings, i which:

"FIG. 1 is a diagram of a circuit having two branch: in parallel which is shown to illustrate the definition the numbers k, l, m, and n;

FIGS. 2 12 are circuit diagrams of preferred en bodiments of reference voltage sources in accordanc with the invention;

FIGS. l3, l4 and 15 show subdivisions of a resistc into elementary resistors for trimming the voltage d vider to adjust ,the circuit in the case of a referenc voltage source built as a monolithic integrated circui and FIGS. 16 and 17 are circuit diagrams of combinatior of a reference voltage source and a following voltag regulator to constitute voltage stabilizers shown as e: amples of application of the manufacturing method the invention.

FIG.'1 shows a diagram in general form of a refe' ence voltage source consisting of two current carryin circuit branches connected in parallel to each othc and carrying an aggregate current I. The first circu branch, shown at the left, contains a series chain of number I of conductively operated diodes and an nun ber k of cascaded Zener diodes. The second circu branch contains, in series, a number m of conductive] operated diodes connected one behind the other,

tage divider composed of two ohmic resistances R IR; and a number n of conductively operated diodes mected one behind the other. One of the places are the two circuit branches are connected together rie so called foot point of the circuit where the anode :he k-th Zener diode and the cathode of the conduc- :ly operated diode which is last in the direction of N of positive current in the second circuit branch. 3 output reference voltage U is taken from the cirt between the common connection point of the two nic resistances R and R and the connection point istituting the above identified foot point of the cirt. The voltage drop across each of the conductively :rated diodes is designated L1,, and the breakdown tage of each of the Zener diodes is designated U plying Kirchhoffs law, the reference voltage U is an by the following expression:

2 temperature dependence of the breakdown volt- U; of the Zener diodes can be expressed with suffint exactitude by the following equation 2 U U 1 +A .d)

which ere T is the absolute temperature, To is the reference iperature, A signifies the temperature coefficient of Zener diode and U represents the breakdown tage at d O, that is, when T To.

Vithin the tolerance range defined by the unavoidamanufacturing scatter of the values of the break- :vn voltage U; of the Zener diodes, the temperature :fficient A of these diodes can be described with adiate accuracy by the following equation otherwise stated,

now, by analogy to equations (2) and (4) there is ned for the temperature dependence of the refere voltage U (d) the following further expression:

If equation (9) is solved for R IR there is obtained for the voltage divider ratio:

If the value for the voltage divider ratio from equation (10) is substituted into equation (7), the following expression is obtained for the reference voltage U (l l Ul(d) (l Ed) From equations (8) and (11) there is then obtained for U (l2) rn If now the value for A; from equation (5) is substituted into equation (12), there is obtained for U z If U is to be independent of U the following relation must hold: v

14 A A, B V

( k-(A-E) k-B(m+n-l)-(EA )'Um If the equation just given is solved for (m n l) k, the result is If this condition is put into equation (13 there is ob tained for U If the reference voltage source is built on a silicon substrate in accordance with monolithic integrated circuit technology, the following values ofA and B are obtained for a particular manufacturing technology and diode geometry and a reference temperature T0 of 300- K:

If it is further assumed that the current through the diodes is 1 mA, the following values are obtained for A and U A 2.86 /K; U 670 mV.

For this case of a current of 1 mA through the diodes there is then obtained:

For other technologies and diode geometries on a silicon substrate, values of A, B, A and U varying only slightly from the above result are obtained so that in those cases also the numerical value on the right hand side of equation (17) lies close to 2.

Since of course m, n, l and k are integers, equation for a current of 1 mA through the diodes, cannot be fulfilled exactly. But since U is a function ofa current through the diode, U can be set at any desired value within certain limits. 1f the current through the diode is l:

By setting U,,,(lo) U and A (lo) A equation (19) becomes:

q lo

In the above equation the following simplifications may be made:

K'To

and

For a particular current through the diodes it can b found that the expression in equation (15) becomes exactly equal to 2.

25 tively operated diodes as follows:

There is thus obtained, from the values for A, B, A an U holding for a particular technology and diode ge ometry, a value for the current at which the expression U00 '(A u is exactly equal to 2, namely I 2.27 mA.

Equations 15) and 16) were derived for a tempera ture coefficient E of the reference voltage U that ma; have any desired value. That means that for all refer ence voltage generator circuits that satisfy the condi tion 15) or in the case of greater accuracy require ments the condition [1+ E (T- To)] In connection with this trimming or balancing opera tion it is to be noted that the conditions (15) and (26) which limit the range of combination of Zener and con ductively operated diodes, are independent of the de ed temperature coefficient E of the reference voltage The circuits of the present invention thus have the )perty that by setting the reference voltage U, by nming the voltage divider R,, R at the temperature to a value specified by equation (l6), the temperae coefficient E of the reference voltage U, is simulta- )usly adjusted to the desired value, so that the tern; rature coefficient of the reference .voltagebecomes lependent of the scatter of the breakdown voltage ues of the Zener diodes inherent in the manufacturprocess and for their temperature coefficients deident on their breakdown voltage.

The circuits that satisfy the equation 1 be produced with conventional manufacturing hniques utilizing discrete partly integrated compoats on printed circuit plates or utilizing thick or thin n techniques on insulating substrates. The monoiicintegrated circuit form of construction, however, ers particular advantages because of the good ther- .l coupling of the elements.

Iircuits that satisfy equation (26') are shown in SS. 2 through 11.

"IO. 2 shows the' simplest embodiment. A single ner diode Z, is provided in the first circuit branch. parallel to the Zener diode Z, there are, in the direcn of flow of positive current, the series connection the voltage divider composed of the two ohmic resislces R, andR, and then, in succession, two conducely operated diodes D, and D all of these forming second circuit branch. In this arrangement, theree, the values k l and m l= have been chosen. )m equation (26) it follows that n 2.

-IG. 3 shows, as a second embodiment, a reference .tage source having its first circuitbranc h, as enurated in the direction ofthe flow of positive current, :onductively operated diode D and a single Zener ide Z, in series. The second circuit branch, enumerng the components in the same order, containsthe tage divider composed of the two ohmic resistances andR, and a succession of three conductively operd diodes D,, D, and D all in series. In this case, -.refore, k I, m O and l 1. From equation (26') ollows that n 3. V "IG. 4 shows a modification of the embodiment of 3. 3. The difference is that in FIG. 4 the two diodes and D, are replaced by a single diode D,, which is nmon to both circuit branches and connected to the called foot point of the circuit. The shared diode D5,, .0 selected that it can operate with the same current isity that is present in the other conductively oper d diodes D, and D I V v I I n the embodiment *shown in FIG. 5 thereisagain y a single Zener diode' Z, inthe first circuit branch. the second circuit branch connected in parallel to sZener diode is the series connection of a first con- :tively operated diode D,, the voltage divider com- ;ed of the two ohmic resistances R, and R and a sec- 1 conductively operated diode D In this case, acdingly, k =1,l= 0 and m 1. From equation (26) ollows that n =1.

'IG. 6 shows a modification of the embodiment of i. 5. The difference is that in FIG. 6 the first conduc tively operated diode D, of FIGJS is constituted by the base-emitter path of aa transistor'T In the embodiment shown in FIG. 7 the first circuit branch contains, enumerating the elements in the direction of the flow of positive current, a conductively operated diode D and a single Zener diode Z,, in series. In parallel thereto, forming the second circuit branch, is the series connection of a first conductively operated diode D,, the voltage divider composed of the two ohmic resistances R, and R and two further conductively operated diodes D and D in'succession. In this case, accordingly, k i 1, I l ancl m I. From equation (26') it follows that n 2. I

FIG. 8 shows a modification of the embodiment of FIG. 7. The difference is that in FIG. 8 two diodes D and D, of FIG. 7 are replaced by a single diode D common to both circuit branches. The shared diode D is so selected that itmay operate at the same current density as do the other conductively operated diodes D, and D t In the embodiment shown in FIG. 9 the first circuit branch is composed of a series connection of a conductively operated diode D and a single-Zener diode-Z,. In parallel .to this series connection is 'the'second circuit branch which iscomposed, enumerating the elements in the order of flow of positive current, of first and second conductively operated diodes D, and D,, the voltage divider composed of the two ohmic resistances R, and R and a further conductively operated diode D all in series. In this case, accordingly, k 1, l= 1 and m 2. From equation (26') it follows that n 1.

FIG. 10 shows a modification of the embodiment of FIG. 9. The difference is that in FIG. 10 the two diodes 0 and D, of FIG. 9 are replaced by a single diode 13 common to both circuit branches The common diode D is again so chosen that it may operate at the same current density as do the other conductively operated diodes D, and D (k= l,l=1, m =2, n=1).

In the embodiment shown in FIG. 11 the first circuit branch again is composed of a single Zener diode Z,. In the second circuit branch there are, enumerated in the direction of positive current flow, the voltage divider composed of the two ohmic resistances R, and R, and two conductively operated diodes D, and D all in serieslk =1, m =l= 0, n 2). The cathode of the second conductively operated diode D, is connected to the anode of the Zener diode Z,. The cathode of the Zener diode Z, is connected to the non-inverting differential input of an. operational amplifier 0,, the output of which is connected both to its inverting differential input and to that end the first ohmic resistance R, of the voltage divider which is not connected to the second ohmic resistance R,.

FIG. 12 shows an embodiment in which two Zener diodes Z, and Z, are provided in the first circuit branch. In the second circuit branch in parallel to the first there are, in the direction of flow of positive current, in series, the voltage divider composed of the two ohmic resistances R, and R, and then, in succession, four conductively operated diodes D,, D D and D,. In this arrangement, therefore, the values X 2 and m =1 0 have been chosen.From equation (26') it follows that n 4. This circuit is analogous to FIG. 2, which is the simplest of the embodiments described above utilizing a single Zener diode. Similarly circuits with two Zener diodes can be developed corresponding to the other preferred circuits described above, and likewise also circuits utilizing three Zener diodes.

In connection with FIGS. 4, 8 and 10, the relation to the other figures was explained by stating that the diode D was common to both branches of the circuit and was counted in determining both I and n for the purpose of equations (15) and (26). Of course, just as there may be more than one of the diodes l and more than one of the diodes n, there may be more than one diode in series instead of the single diode D If the number of these diodes is designated p, then the con ductively operated diodes remaining in the first circuit branch will number I p, where is at least as great as p, and the number remaining between the resistor R and the first diode D will likewise be It p, where n is at least as great as p. If We want to rewrite equation (15) to bring in diodes p separately, however, we will find that when lp is subtracted from the sum of m and n p, the ps cancel out. Consequently, for circuits like FIGS. 4, 8 and 10, the criterion of equations (15) and (26') can be stated precisely the same way treating the diode D as not included either in l or n, as they can be stated treating that diode as included in both 1 and n. When the diode D and anymore like it are treated as not included in either i or n, the language of a state ment stating the invention as embodied in FIGS. 4, 8 and 10 is somewhat simpler, although this defined n, for example, in FIG. 4 in the same way as in FIG. 2 and treats FIG. 4 as a case of l 0, m 0 and n 2, with the'further fact that p 1, which is irrelevant to equations and (26), (since ifp is added to both land n it drops out of the equation).

If in construction of any of the circuits shown in FIGS. 2-12 the monolithic integrated circuit form of construction is used, it would be natural to provide the conductively operated diodes in the form of emitter diodes and the resistances R and R by means of a base diffusion zone, in which case the unavoidable path resistance of the conductively operated diodes will constitute a portion of the resistance R or of the resistance R or both, as the case may be, and these path resistances will all have the same thermal behavior.

In conventional circuits, trimming can be done by means of a potentiometer. A more exact procedure is the trimming of film resistances by means of a sand jet (sandblasting) or a laser beam (easer beam cutting) or by electrochemical etching or oxidation (electrochemical action) of the resistances R R or both.

In' monolithic integrated circuits it is convenient to subdivide the resistor R the resistor R or both, for purposes of trimming. The resistor in question may be separated into a number of component resistors and all but one of them short-circuited by conductive bridges. FIG. 13 shows such a development of the resistance R,. The component resistors are designated R R R R R R represents the smallest possible value for the resistor R and is not short-circuited. It is advantageous to provide the resistance values of the shortcircuited component resistors R R R in such a way that these values are in the progression 1 2 4 8 The more accurately the reference voltage U is to be set, the more component resistors are necessary. The trimming process is desirably combined with the now conventional premeasurement procedure applied to the chips at a wafer test station of the manufacturing process. In that case the measuring apparatus of the wafer test equipment measures the actual value of the reference voltage U A computer coupled to th measuring equipment calculates, from the differenc between the measured value and the desired valur what combination of component resistors must b added in circuit to the component resistor R or R 2 the case may be (the minimum operating resistors), i order to reach the prescribed design value at whic equation (16) will be fulfilled. The conductive bridge to be removed, for example B and B in FIG. 13, at then burned away with a current pulse. Although th operation increases the effective resistance in the ci: cuit, it may be referred to properly as trimming" th voltage divider, since it brings the voltage divider to desired permanent condition, and the word trimming is herein used in a sense broad enough to comprehen the operation just described.

If resistances of'relatively low ohmic value are nece: sary, these can be provided by connecting in parallr two or more resistors R R all of the same gr ometry, in accordance with FIG. 14.

With the configuration of FIG. 15 it is possible I: separating off component resistors of high ohmic valu to make very small changes of the effective resistanci If, for example, R has the value of 200 ohms and R, 1,800 ohms, the only value of this combination changed from ohms to 200 ohms if the bridge B cut.

FIG. 16 shows an example of the application of th source of reference voltage according to the preset invention as part of a circuit for stabilizing a voltagi that circuit consisting of the source of reference vol age and a voltage regulator. U is the unstabilized inpl voltage and U is the stabilized output voltage. The ui stabilized input voltage U,,- is applied to the supply vol age terminals 1 and 2 of an operational amplifier 0 The noninverting input of the operational amplifier l is connected to the reference voltage U, taken from tl"v reference voltage source at the common connection the resistors R and R of the voltage divider of the re erence voltage source. The reference voltage source, i accordance with the invention, has a diode combin: tion in its two circuit branches which satisfies equatio (15). The inverting input of the operational amplifu 0 is connected to the common connection point of tt two ohmic resistances R and R.,, which constitute second voltage divider. The output 3 of the operation amplifier 0 is connected with the free end of the resi tor R The free end of the resistor R is connected 1 the second terminal 2 of the supply voltage and also 1 the connection point 4 of the two circuit branches 1 the reference voltage source, where the k-th Zen diode of the first circuit branch is connected to the n-1 conductively operated diode of the second circu branch (this illustrated embodiment is the connectic point of the single Zener diode 2, with the second (:01 ductively operated diode D The stabilized outpi voltage U A of the voltage stabilizer appears betwee the output 3 of the operational amplifier 0 and the seond terminal 2 of the supply voltage of the operation amplifier.

For further clarification a voltage stabilizer is show in FIG. 17 in which the operational amplifier I.) of Fl( 16 is made up of the differential amplifier formed t the two transistors T and T and the resistor R ti gether with the transistor T driven by the differenti amplifier by means of the resistor R 1 the case of heretofore known voltage stabilizers nposed along the lines of FIG. 16 and FIG. 17 with using reference voltage sources of the present in tion, the stabilized output voltage U,, is either not usted by trimming to the desired design value or else djusted by changing the second voltage divider R 1 a further application of the invention, however, stabilized output voltage U of the circuits shown IGS. 16 and 17 is trimmed to bring it to the desired cifications, not in the usual way by trimming the :age divider R R but rather by trimming of the :age divider R R of the reference voltage source. 5 operation proceeds as follows: from the desired tperature coefficient of the stabilized output voltage which is the same as the temperature coefficient E he reference voltage U the reference voltage U the reference temperature T is calculated by refere to equation (16). The second voltage divider R is then so dimensioned that it provides the desired put voltage U, when the reference voltage has the re U This is the case when the divider ratio is itransistor can be used as a Zener diode. The con-" tively operated diodes can be diodes having pn- :tions, diodes formed by metal-to-semiconductor tacts or partly pn-junction diodes and partly al-to-semiconductor diodes. Each of these" diodes also be provided by the base-emitter path of a tran- Jr connected for conductive operation, that is, :d in the direction of conduction. In this last men- .ed case, the collectors of these transistors can in le'cases be utilized for further purposes, for eitam-' onnection with FIG. 6. I f 'e claim:

A method of making a source of reference voltage" ing a desired temperature coefficient of said refervoltage and containing at least one Zener diode, number of Zener diodes being designated k, and a lber of conductively poled diodes, possibly zero and gnated 1, connected in series with said Zener di- (s) and comprising also a shunt circuit branch conted in parallel with said Zener diode(s) and the esaid conductively poled diodes, composed ofa reve voltage divider having an intermediate tap prorig an output terminal for a reference voltage (U in series with said voltage divider, a number of iuctively poled diodes, possibly zero and desigd m, connected between a first pole of a current )ly source and said voltage divider and also at least conductively poled diode, the number thereof g designated n, connected between said voltage dir and a second pole of said current supply means, :h method comprises the steps of:

4s forgeneration of -a constantcurrent, as indicated v I is exactly'satisifed for the particularnumbers l, k, v m 5 and n of diodes contained in said twoparallel circuits.

making a source of reference voltage having components as above set forth in such a way as to approximate a design criterion of without regard to the scatter of Zener breakdown voltages of Zener diodes used, said scatter being within a reasonable manufacturing tolerance, and

progressively modifying the resistance values of the resistances (R R of said voltage divider and thereby trimming said voltage divider at a predetermined reference temperature T until the value U that the output reference voltage U, has at the aforesaid reference temperature T reaches the predetermined value where I j I A is the constant portion of the temperature coefficient of the Zener diodes in "K, j A is the temperature coefficient of the conductively poied diodes in their conductive. state, in "K B is the voltage-dependent portion of the'temperature coefficient of the Zener diodes in volts per K, U is the voltage drop per diode in volts across the conductively poled diodes during conduction at the reference temperature T,,'and v E is said desired temperature coefficient of said reference voltage U in 'K Q-QL." I I I 2. A .method as defined in claim 1 in which the aforesaid step preceding the step of modifying voltage divider resistance values is carried out by providing for the occurrence of a voltage drop U per diode across the conductively poled diodes and fora temperature coefficient A of the. conductively poleddiodes so dition 12 van-4..)

3; A method as defined in claim 1 in which the afore 'said step preceding the step of modifying voltage divider resistance values is carried out by constituting a circuit in which the number ofdiodes in the two parallel circuits designated by l, k, m and n satisfies the condition lla u) voltage divider (R R is carried out on a monolithic integrated circuit chip.

6. A method as defined in claim 5 in which said voltage divider (R,, R is trimmed during the premeasurement of the chip on a wafer test equipment.

7. A method as defined in claim 6 in which at least one of the resistors (R R constituting said voltage divider is subdivided into at least two resistor portions for purposes of trimming and that the trimming step is carried out by the interruption of at least one conduction path by which said resistor portions were originally interconnected.

8. A method of manufacture as defined in claim 7 in which the resistance values of said resistor portions utilized in the trimming step are related to each other in the progressive ratio 1 2 4 8 l6 32 9. A method as defined in claim 1 in which the step of trimming a voltage divider is performed with a voltage regulator connected with said source of reference voltage as made prior to the trimming step, so as to form a voltage stabilizer together, said voltage stabi lizer providing a stabilized output voltage U at the output of a second voltage divider (R R and in which the desired stabilized voltage U is obtained by variation of the first voltage divider (R R in the compleand the reference voltage U at the reference temperature T is defined as satisfying the condition ln na where A is the constant portion of the temperature coefficient of the Zener diodes in K,

A is the temperature coefficient of the conductively poled diodes in their conductive state, in K,

E is said desired temperature coefficient of said reference voltage U in K and U is the voltage drop per diode in volts across the conductively poled diodes during conduction at the reference temperature T and the temperature coefficient E of the reference voltage U, is set equal to the desired temperature coefficient of the stabilized output voltage U,..

10. A method as defined in claim 1 in which said voltage divider is trimmed progressively by removal of portions of the resistors of said voltage divider at least in part by laser beam cutting.

11. A method as defined in claim 1 in which said voltage divider is trimmed progressively by modification of portions of the resistors of said voltage divider at least in part by electrochemical action.

12. A method of making a source of reference voltage having a desired temperature coefficient of said reference voltage and containing at least one Zener diode, the number of Zener diodes being designated k, and a number of conductively poled diodes, designated 1, connected in series with said Zener diode(s) and comprising also a shunt circuit branch connected in parallel with said Zener diode(s) and the aforesaid con ductively poled diodes, composed of a resistive voltagr divider having an intermediate tap providing an outpu terminal for a reference voltage (U and, in series witl said voltage divider, a number of conductively poler diodes, possibly zero and designated m, connected be tween a first pole of a current supply source and sair voltage divider and also at least one conductively poler diode, the number thereof being designated n, con nected between said voltage divider and a second polr of said current supply means, at least one of said las mentioned diodes being a dual-function diode by virtur of being also connected in cascade with said Zener di 0de(s) and counting also as one of said first mentioner group of conductively poled diodes, the number 0 which is designated 1, which method comprises the steps of:

making a source of reference voltage having compo nents as above set forth in such a way as to approxi mate a design criterion of without regard to the scatter of Zener breakdown volt ages of Zener diodes used, said scatter being within 2 reasonable manufacturing tolerance, and

progressively modifying the resistance values of the resistances (R R of said voltage divider ant thereby trimming said voltage divider at a predetermined reference temperature T until the value U that the output reference voltage U, has at the aforesaid reference temperature T, reaches the predetermined value A A Um Um 7:?

where A A is the constant portion of the temperaturecoeffici ent of the Zener diodes in K A is the temperature coefficient of the conductively poled diodes in their conductive state, in "K B is the voltage-dependent portion of the temperature coefficient of the Zener diode(s) involts pel K, J U is the voltage drop per diode in volts across the conductively poled diodes duringconduction at the reference temperature T,,, and I f' E is said desired temperature coefficient of said reference voltage U in K' i i 13. A method as defined -in claim 12in which the aforesaid step preceding the step of modifying voltage divider resistance values is carried out by constituting a circuit in which at least one aforesaid dual-function diode is connected between the pole of the current source from which the output voltage at the voltage divider tap is measured and a function at which the current through said Zener diode(s) joins the current through said shunt circuit, said dual-function diode being counted both as one of the diodes determining the said number land as one of the diodes determining the said number n.

14. A method as defined in claim 13 in which the aforesaid step preceding the step of modifying voltage divider resistance values is carried out by providing for occurrence of a voltage drop U across the conctively poled diodes and for a temperature coefficit A of the conductively poled diodes so chosen by 'erence to the current density that the condition exactly satisfied for the particular numbers I, k, m :l n of diodes contained in said two parallel circuits. .5. A method as defined in claim 13 in which the vresaid step preceding the step of modifying voltage 'ider resistance values is carried out by constituting ircuit in which the number of diodes in the two par- :l circuits designated by l. k, m and n satisfies the adition least approximately equals 2.

,6. A method as defined in claim 13 in which said .tage divider is trimmed progressively by removal of rtions of the resistors of said voltage divider at least part by sandblasting.

.7. A method as defined in claim 13 in which said tage divider is trimmed progressively by removal of rtions of the resistors of said voltage divider at least part by laser beam cutting.

,8. A method as defined in claim 13 in which said tage divider is trimmed progressively by modifican of portions of the resistors of said voltage divider least in part by electrochemical action.

.9. A method as defined in claim 13 in which a refer- :e voltage source is produced in monolithic inteltfid circuit form and in which the trimming of said tage divider (R,, R is carried out on a monolithic egrated circuit chip.

20. A method as defined in claim 19 in which said tage divider (R,, R is trimmed during the premeas- :ment of the chip on a wafer test equipment.

.1. A method as defined in claim 13 in which at least a of the resistors (R R constituting said voltage ider is subdivided into at least two resistor portions for purposes of trimming and that the trimming step is carried out by the interruption of at least one conduction path by which said resistor portions were originally interconnected.

22. A method of manufacture as defined in claim 21 in which the resistance values of said resistor portions utilized in the trimming step are related to each other in the progressive ratio 1 2 4 8 l6 32 23. A method as defined in claim 13 in which the step of trimming a voltage divider is performed with :1 voltage regulator connected with said source of reference voltage as made prior to the trimming step, so as to form a voltage stabilizer together, said voltage stabilizer providing a stabilized output voltage U at the output of a second voltage divider (R R and in which the desired stabilized voltage U,, is obtained by variation of the first voltage divider (R R in the completion of the manufacture of the source of reference voltage as aforesaid, and in which, further, the second voltage divider (R R.) has a resistance ratio defined as n U4 1 4 IG and the reference voltage U at the reference temperature T, is defined as satisfying the condition coefficient of the stabilized output voltage U 

1. A method of making a source of reference voltage having a desired temperature coefficient of said reference voltage and containing at least one Zener diode, the number of Zener diodes being designated k, and a number of conductively poled diodes, possibly zero and designated l, connected in series with said Zener diode(s) and comprising also a shunt circuit branch connected in parallel with said Zener diode(s) and the aforesaid conductively poled diodes, composed of a resistive voltage divider having an intermediate tap providing an output terminal for a reference voltage (U1) and, in series with said voltage divider, a number of conductively poled diodes, possibly zero and designated m, connected between a first pole of a current supply source and said voltage divider and also at least one conductively poled diode, the number thereof being designated n, connected between said voltage divider and a second pole of said current supply means, which method comprises the steps of: making a source of reference voltage having components as above set forth in such a way as to approximate a design criterion of
 2. A method as defined in claim 1 in which the aforesaid step preceding the step of modIfying voltage divider resistance values is carried out by providing for the occurrence of a voltage drop UDo per diode across the conductively poled diodes and for a temperature coefficient AD of the conductively poled diodes so chosen by reference to the current density that the condition
 3. A method as defined in claim 1 in which the aforesaid step preceding the step of modifying voltage divider resistance values is carried out by constituting a circuit in which the number of diodes in the two parallel circuits designated by l, k, m and n satisfies the condition
 4. A method as defined in claim 1 in which said voltage divider is trimmed progressively by removal of portions of the resistors of said voltage divider at least in part by sandblasting.
 5. A method as defined in claim 1 in which a reference voltage source is produced in monolithic integrated circuit form and in which the trimming of said voltage divider (R1, R2) is carried out on a monolithic integrated circuit chip.
 6. A method as defined in claim 5 in which said voltage divider (R1, R2) is trimmed during the premeasurement of the chip on a wafer test equipment.
 7. A method as defined in claim 6 in which at least one of the resistors (R1, R2) constituting said voltage divider is subdivided into at least two resistor portions for purposes of trimming and that the trimming step is carried out by the interruption of at least one conduction path by which said resistor portions were originally interconnected.
 8. A method of manufacture as defined in claim 7 in which the resistance values of said resistor portions utilized in the trimming step are related to each other in the progressive ratio 1 : 2 : 4 : 8 : 16 : 32 : ... .
 9. A method as defined in claim 1 in which the step of trimming a voltage divider is performed with a voltage regulator connected with said source of reference voltage as made prior to the trimming step, so as to form a voltage stabilizer together, said voltage stabilizer providing a stabilized output voltage UA at the output of a second voltage divider (R3, R4), and in which the desired stabilized voltage UA is obtained by variation of the first voltage divider (R1, R2) in the completion of the manufacture of the source of reference voltage as aforesaid, and in which, further, the second voltage divider (R3, R4) has a resistance ratio defined as
 10. A method as defined in claim 1 in which said voltage divider is trimmed progressively by removal of portions of the resistors of said voltage divider at least in part by laser beam cutting.
 11. A method as defined in claim 1 in which said voltage divider is trimmed progressively by modification of portions of the resistors of said voltage divider at least in part by electrochemical action.
 12. A method of making a source of reference voltage having a desired temperature coefficient of said reference voltage and containing at least one Zener diode, the number of Zener diodes being designated k, and a number of conductively poled diodes, designated l, connected in series with said Zener diode(s) and comprising also a shunt circuit branch connected in parallel with said Zener diode(s) and the aforesaid conductively poled diodes, composed of a resistive voltage divider having an intermediate tap providing an output terminal for a reference voltage (U1) and, in series with said voltage divider, a number of conductively poled diodes, possibly zero and designated m, connected between a first pole of a current supply source and said voltage divider and also at least one conductively poled diode, the number thereof being designated n, connected between said voltage divider and a second pole of said current supply means, at least one of said last mentioned diodes being a dual-function diode by virtue of being also connected in cascade with said Zener diode(s) and counting also as one of said first mentioned group of conductively poled diodes, the number of which is designated l, which method comprises the steps of: making a source of reference voltage having components as above set forth in such a way as to approximate a design criterion of
 13. A method as defined in claim 12 in which the aforesaid step preceding the step of modifying voltage divider resistance values is carried out by constituting a circuit in which at least one aforesaid dual-function diode is connected between the pole of the current source from which the output voltage at the voltage divider tap is measured and a function at which the current through said Zener diode(s) joins the current through said shunt circuit, said dual-function diode being counted both as one of the diodes determining the said number l and as one of the diodes determining the said number n.
 14. A method as defined in claim 13 in which the aforesaid step preceding the step of modifying voltage divider resistance values is carried out by providing for the occurrence of a voltage drop UDo across the conductively poled diodes and for a temperature coefficient AD of the conductively poled diodes so chosen by reference to the current density that the condition
 15. A method as defined in claim 13 in which the aforesaid step preceding the step of modifying voltage divider resistance values is carried out by constituting a circuit in which the number of diodes in the two parallel circuits designated by l, k, m and n satisfies the condition
 16. A method as defined in claim 13 in which said voltage divider is trimmed progressively by removal of portions of the resistors of said voltage divider at least in part by sandblasting.
 17. A method as defined in claim 13 in which said voltage divider is trimmed progressively by removal of portions of the resistors of said voltage divider at least in part by laser beam cutting.
 18. A method as defined in claim 13 in which said voltage divider is trimmed progressively by modification of portions of the resistors of said voltage divider at least in part by electrochemical action.
 19. A method as defined in claim 13 in which a reference voltage source is produced in monolithic integrated circuit form and in which the trimming of said voltage divider (R1, R2) is carried out on a monolithic integrated circuit chip.
 20. A method as defined in claim 19 in which said voltage divider (R1, R2) is trimmed during the premeasurement of the chip on a wafer test equipment.
 21. A method as defined in claim 13 in which at least one of the resistors (R1, R2) constituting said voltage divider is subdivided into at least two resistor portions for purposes of trimming and that the trimming step is carried out by the interruption of at least one conduction path by which said resistor portions were originally interconnected.
 22. A method of manufacture as defined in claim 21 in which the resistance values of said resistor portions utilized in the trimming step are related to each other in the progressive ratio 1 : 2 : 4 : 8 : 16 : 32 : ... .
 23. A method as defined in claim 13 in which the step of trimming a voltage divider is performed with a voltage regulator connected with said source of reference voltage as made prior to the trimming step, so as to form a voltage stabilizer together, said voltage stabilizer providing a stabilized output voltage UA at the output of a second voltage divider (R3, R4), and in which the desired stabilized voltage UA is obtained by variation of the first voltage divider (R1, R2) in the completion of the manufacture of the source of reference voltage as aforesaid, and in which, further, the second voltage divider (R3, R4) has a resistance ratio defined as 